Enhancement of electrochemical capacitance by tailoring the geometry of TiO2 nanotube electrodes

The electrochemical properties of different aspect ratio nanotube electrodes have been investigated. The fabrication of nanotube electrodes is done by varying the applied voltage in electrochemical anodization. The nanotube electrode (S40) with aspect ratio 45 yields an areal capacitance of 1.78 mF/cm(2), (for a scan rate of 5 mV/s) which is 4 times higher than nanotube electrode with aspect ratio 14 (S10). Electrochemical treatment of the nanotube electrodes is carried out for further enhancement of capacitance. The electrochemically treated nanotube electrode (E-S40) provides an areal capacitance of 7.4 mF/cm(2) for a scan rate of 5 mV/s and 4.2 mF/cm(2) at a scan rate of 500 mV/s. The electrodes exhibit high capacitance retention at higher current densities and good long term stability. Electrochemical impedance spectroscopy reveals the effect of electrochemical treatment on the carrier density and the impedance of the nanotube electrodes. (C) 2015 Published by Elsevier Ltd.